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DOSE RATE IN A CYLINDRICAL CREW
C OM P R R TM E N T RES U LT IN G FROM
AIR-SCATTERED GAMMA RAYS
C. D. Zerby
The problem of determining the contribution of
air-scattered gamma rays to the dose rate in a
cylindrical crew compartment has been separated
into two parts. In the first part the gamma-ray flux
in air at various distances from an idealized point
source is to be obtained. In the second part the
flux is considered to be the source at the outside
surface of the crew compartment, and the dose rate
qt several arbitrary positions inside the crew com-
partment is to be determined. The results ob
tained for both parts of the problem will then be
integrated. The complete problem is a joint effort
of the Wright Air Development Center (WADC) and
the Oak Ridge National Laboratory, with the bulk
of the computation to be done by the Monte Carlo
method and to be performed at WADC.
The first part of the problem has been programed
and coded for calculation on a type 1103 automatic
computing machine, and test cases are being run
in preparation for a complete parameter study. In
this part of the problem the angular distribution and
the energy spectrum of air-scattered gamma rays
will be determined at several separation distances
from a point source. The source will be considered
to be monoenergetic and to be emitting gamma rays
symmetrically about the source-detector axis in a
conical shell. The parameter study will, therefore,
include o survey of various separation distances,
source energies, and apex angles of the conical
shell beam. With the results of the parameter study
it will be possible to obtain the radiation current
at each separation distance for any point source
which emits gamma rays symmetrically about the
source-detector axis with any energy spectrum.
Although the density of air at sea-level conditions
will be used in the calculations, it will be possible
to obtain the results at any altitude (different
density of the air) by using the transformations
developed for this purpose and reported below.
The analysis and procedure for the second part
of the problem are complete and have been re-
* ported. Results of the calculation will include
the detailed angular distribution and energy spec-
W
5.1. SHIELDING THEORY
C. D. Zerby
trum of the radiatior: entering the crew-compartment
cavity and the dose rate at various positions in
the cavity, A parameter study will be made for
various thicknesses of lead and polyethylene in
the crew-compartment walls.
RADIATION FLUX TRANSFORMATION AS A
FUNCTION OF DENSITY OF AN INFINITE
MEDIUM WITH ANISOTROPIC
POINT SOURCE‘S
C. D. Zerby
The transformation of flux, current, or dose rate
as a function of density of an infinite homogeneous
medium with anisotropic point sources can be
derived directly from the Boltzmann equation.2
This transformation is particularly of interest be-
cause of the many calculations which use this
geometry, and, in addition, it provides a means of
transforming the Tower Shielding Facility (TSF)
sea-level dose-rate data to data at any altitude.
The transformation is obtained by writing the
Boltzmann equation for an anisotropic point source
at the origin in nondimensional form:
where
-9
!2 = unit vector,
E = energy,
+
Eo = arbitrary fixed energy,
os@) = microscopic scattering cross sec-
tion at energy E, cm2,
’C. D. Zerby, A Monte Grlo Method of Calculating
the Response of a Point Detector at an Arbitrary Posifion
Inside a Cylindrical Shield, ORNL-2105 (June 12, 1956).
2C. D. Zerby, Radiation Flux Transformations as a
Function of Density of an Infinite Medium with Aniso-
tropic Point Sources, ORNL-2100.
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